Electric valve control for dynamoelectric machines



Now 25, 1947. E. E. MOYER ET AL 2,431,578

ELECTRIC VALVE CONTROL FOR DYNAMOELECTRIC MACHINES Filed March 28, 1946 Inventors: Elmo E. Meyer, ,Donald Eldred,

A f I 1 The iPAtto -n ey Patented Nov. 25, 1947 l UNITED STATES, PATENT OFFICE ELECTRIC VALVE'CONTROL FOR DYNAMO- ELECTRIC MACHINES Elmo E. Moyer, Scotia, and Donald Eldred, Schenectady, N. Y., assignors to General Electric Company, a corporation oi. New York Application March 28, 1946,- Serial No. 657,879

teams. (or. 318-297) This invention relates to control systems, more the supply conductors 4 and 5. These supply conparticularly to systems for controlling the operaductors may be energized with alternating voltage tions of electric motors, and it has for an object of a suitable value, c. g. 230 volts.

the provision of a simple, reliable, eflicient and The motor I is illustrated as a series motor havinexpensive control system of this character. 5 .ing a split series field winding comprising two on- More particularly, the invention relates to moposing coils lb and lo; It may be assumed that tor control systems in which a reversible direct energization of the coil lb efiects rotation in the current motor is supplied by suitable electric valve 7 forward direction and that energlzation of the apparatus from a source of alternating voltage, coil lc effects rotation in the reverse direction. and a more specific object of-the invention is the; 10 Although electric valves 2 and 3 may be of any provision of a control system in which the magnisuitable type; they are preferably of the triode .tude and direction of rotation of the motor is contype having an anode, a cathode, and a control trolled in response to changes in the magnitude of grid, and having a small quantity of a gas, such asignal voltage. vas mercury vapor or argon within the envelope. In carrying the invention into effect in one he p s this gas converts the usual p form thereof, the armature'of a reversible motor electronic discharge to an arc st 50 t at is connected to a source of alternating voltage the valve becomes a grid controlled arc rectifier. through a pair of half wave rectifying valves. he grid has control only of the startin of the One of theseivalves supplies half wave current imcharge. However, by varyin he fi ng p in pulses to the motor for rotation in one direction i.,e. the time in the positive half cycle or the anand the other furnishes half wave current imode voltage at which the grid voltage attains the pulses for rotation in the opposite direction, Th critical value necessary to initiate current flow in amount of current supplied by each of these rectithe anode-cathode circuit, the average value of tier valves is controlled by means of an individual the current which flows in the output circuit can capacitor. Two pair of controlvalves, one pair be v l' f the firing Point Occurs at a for each of the capacitors, are provided for varythe beginning of the positive'half cycle of the aning the charges on the capacitors. One of each ode voltage, maximum current will flow in the pair of the control valves is a grid controlled output circu t- If e firing point occurs between valve. The grid of one of these grid controlled the 90 degree and 180 degree point, the current valves is connected to a source of adjustable volt- 0 flow will be a minimum or zero. For intermediate age. A signal voltage is supplied to the grid of firing points the output will have corresponding the other grid controlled valve. The cathodes of intermediate values.

the two grid controlled valves are connected to- As shown in the drawing, the upper terminal gether and through a common resistor to one side or the armature la is connected to the supply of the alternating voltage source. An increase of conductor 4 and the lower'terminal is connected the signal voltage above a predetermined value to the junctionpoint of the two field windings .lb has theefiect of increasing the conductivity of one and, Ic.' The free terminals of'the field coils lb of the grid control valves, thereby to increase the, and la are connected to the anodes 2a and 3a recurrent conducted by one of the rectifier valves. spectively of the "rectifier valves 2 and 3 of which correspondingly, a decrease of the signal voltage 40, the cathodes b and 3b respectively are conbelow this predetermined value decreases the nected to the supply'conductor I.

conductivity of the first grid controlled valve and /For the purpose or controlling the firing point increases the conductivity of the second grid conof the valve 2, a capacitor 8 is provided together trolled valve to increase the current conducted by with a pair-oi control electric valves 1 and 8. One the other rectifiervalve. 5terinin-a1pr the capacitor 8 is connected to the v For a better a d more complete understanding supply conductor 5 and the other terminal 6a is oi. the invention; references'ho'uld now be had to connected through a protective resistor 9 to the the following specification and to the accompanygrid 2c, ,The terminal- Iia is also connected ing drawing of which Fig.1 is a simple, diagram-- through valve 1 and a series resistor to the oppo matical illustration of an embodiment of the insite supply conductor 4. Thus, the capacitor 8 is vention, and Fig. 2 is a detail of a modification; connected across the cathode 2b and the grid-2c Referring now to the drawing, the armature la of valve 2 so that any voltage which exists across of a reversible direct current motor lisconnected the capacitor is appliedj'between the cathode 2b in circuit with the anode-cathode conducting path and grid 20. I i I of a pair of rectifier electric valves 2 and 3 across 56 Preferably the valve 1 is a diode valve having an anode la and a cathode 1b. As shown in the drawing, a triode valve having its grid connected to the anode may be employed to provide diode operation. The valve 8 is a controlled valve having an anode 8a, a cathode 8b and a control grid 80. This valve is connected in a circuit which extends from the supply conductor through capacitor 6, anode-cathode circuit of valve 8 and adjustable resistor III to the supply conductor 4. It is thus connected in parallel with the diode valve 1 and is reversely connected with respect thereto, 1. e. its anode 8a is connected to the cathode lb of valve 1 and its cathode 8b is con--v nected through the resistor III to the supply conductor 4 to which the anode la of valve 1 is connected;

Owing to the reverse connection of the two valves 1 and 8, both halves of the alternating voltage wave of the supply conductors 4, 5 are applied to capacitor 6 and thus the capacitor is alternately charged with voltages of opposite polarity. During the half cycle in which the valve 1 conducts, the voltage of the terminal 5a tends to become positive and during the succeeding half cycle in which the valve 8 conducts, the capacitor tends to discharge and to become recharged to the opposite polarity so that the terminal 6a tends to become negative. If the valves 1 and 8 conduct equally, the voltage across the capacitor 6 is an alternating voltage having no direct current component. This alternating voltage will lag the anode voltage of the valve 2 by approximately 90 degrees if the reactance of the capacitor 6 is small compared to the equivalent resistance of the valves 1 and 8. However, if the amounts of current conducted by the two reversely connected control valves are unequal, the alternating voltage across the capacitor 6 will have a direct current component, the polarity of which depends upon which of the two oppositely poled currents tends to be the greater and the magnitude of which depends upon the difference in the amounts of the two currents. Thus, if the valve 1 conducts, in effect, more current than valve 8, the polarity of the net direct current component across the capacitor 6 will be such that the terminal 611 becomes positive with respect to the voltage of the supply conductor 5. Conversely, if the valve 8 conducts more current than valve 1 conducts, the voltage of the terminal 6a becomes negative with respect to the supply conductor 5. Since the grid 20 of the valve 2 is connected to the terminal 6a, the effect of varying the direct current component of the voltage across the capacitor 5 is to vary the firing point of the valve 2. Thus, as the direct current component increases in a direction to make the terminal 5a more positive, the firing point of valve 2 is advanced and the amount of current supplied by valve 2 to the armature and field coil lb is correspondingly increased. Conversely, as the direct current component is varied in a direction to make the terminal 6a less positive, the firing point of valve 2 is retarded and the amount of current supplied to the armature and field coil is correspondingly decreased.

Similarly a capacitor ll is connected between the cathode 3b and grid 30 of valve 3. A protective resistor I2 is connected between the grid and the terminal Ila of the capacitor. For the purpose of controlling the charge on the capacitor II, a pair of inversely connected control valves l3 and I4 are provided. As shown, the valve I3 is a triode valve with its grid connected to the anode to provide diode operation, and the valve I4 is a controlled valve having an anode a, a cathode Nb, and a control grid llc. The anode No of valve l4 and the cathode lib of valve II are connected together to the terminal lla of the capacitor. The control valves l3 and I4 function to control the charge on the capacitor ll and thus to control the firing point of the valve 3 in the same manner that the valves 1 and 8 control the firing point of the valve 2 as explained in the foregoing,

The cathode Nb of control valve i4 is connected to the cathode 8b of control valve 8 and through the common adjustable resistor ill to the supply conductor 4, and the control grid He is connected to a point of adjustable voltage. For this purpose a voltage divider comprising the resistors l5, l6 and l'! is connected across the supply conductors 4 and 5 and the grid He is connected to the slider lie of the adjustable resistor l8. 1

For the purpose of controlling the valve 8 a signal voltage is derived from the voltage drop across the resistors l8 and IS with which 9. variable control device such as the photo-electric cell 20 is connected in circuit. As shown, a plurality of resistors 2|, 22 and 23 are connected across the supply conductors 4, 5 and the anode of the photo-electric cell 20 is connected through a resistor. to the junction point of the resistors 22 and 23. The signal voltage which appears across the resistors l8 and I9 is amplified by means of the electric valve 25 of which the anode 25a is connected through a resistor 26 to the supply conductor 5 and the cathode 25b is connected tothe junction point of the resistors 2| and 22. The grid 250 of valve 25 is connected to the cathode of the photo-electric cell 20. Thus, the difference between the voltage drop across the resistor 2i and the signal voltage across the resistors l8 and I9 is applied between the cathode 25b and grid 25c of valve 25.

The initial grid bias of valve 25 is so adjusted that with a predetermined amount of light falling upon the photo-electric cell 20 the signal voltage drop across resistors II and I9 is such that the valve 25 is conducting approximately in mid range.

The grid of the control valve l is connected to the anode 25a of the amplifier, valve through a suitable protective resistor 21 so that the grid to cathode voltage of valve 8 is made to depend upon the voltage difference between the voltage drop across the resistor l0 and the drops across resistor 2| and valve 25.

Initially, the grid biases of the valves 8 and I4 are so adjusted that with the valve 25 conducting in mid range, the valves 8 and H are also conducting at such a point in their useful ranges that the firing points of the valves 2 and I are retarded beyond the degree point. This results in minimum or zero current being supplied by the valves 2 and 3 to the armature of the motor la and the motor is at rest.

With the foregoing understanding of the elements and their organization, the operation of the system will be readily understood from the 7 following detailed description:

.conductivity of valve 8 decreases.

' minal No is negative.

drop across the resistor 28 thereby to make the voltage or the grid 80 of valve 8 increasingly negative with respect to the voltage of its cathode. This results in decreasing the conductivity of the valve 8 with respect to the conductivity of the valve 1 so that in effect more charging current is supplied to the capacitor 8 by the valve 1 than is supplied by the valve 8. Consequently, there appears across the capacitor 8 a component of direct voltage of which the polarity is positive at the terminal 8a. This component of direct voltage advances'the firing point of the valve 2 thereby rendering the valve conductive and causing voltage impulses to be supplied to the armature la and field coil I b of the motor during those half cycles of supply voltage in which thevoltage of the supply conductor 4 is positive.

The decreased conductivity of valve 8 reduces the voltage drop across the common cathode resistor II! with the result that the voltage of the cathode l4b is correspondingly reduced, 1; e., made increasingly negative with respect to the voltage of the grid Me. The decreased voltage drop cathode resistor I 0 renders the voltage or the cathode l4b increasingly positive with respect to the voltage of the grid I40. This correspondingly decreases the conductivity of the valve 44 because the voltage of the grid He remains constant. Consequently, the conductivity of the valve I4 is decreased by approximately the same amount that the conductivity of the valve 8 is increased. 7 As a result of the decreased conductivity of the valve M, the polarity of the direct component voltage across the capacitor ll becomes more positive at the terminal Ila thereby advancing the firing point of the valve 3. This causes current to be supplied to the armature.

and series field coil lc thereby effecting rota-.

tion of the motor in a reverse direction.

across the resistor I 0 also makes the voltage of v the cathode 8b increasingly negative with respect to the voltage of grid 80. However, since the voltage of the grid I40 remains constant,

the conductivity of valve I4 increases while the The-net result is that the conductivity ofthe valve I4 is increased approximately to the same extent that the conductivity of the valve 8 is decreased,

Since the conductivity of valve l3 remains constant while the conductivity of valve I4 is increasing, more charging currentis supplied by the valve l4 to the capacitor H than is supplied by the valve i3. Consequently, there appears across the capacitor II a direct current component voltage of which the polarity'at the ter to the armature la and field coil lb or the motor is correspondingly increased. Similarly, it the amount of light falling on the cathode of the cell 20 is decreased, the firing point of the valve 2 is retarded and the amount of current supplied to the motor I by the valve 2 is correspondingly decreased.

If the light falling on the cathode of the photoelectric cell is decreased to such an extent that the signal voltage drop across the resistors I8 and I9 falls below the predetermined value, the conductivity 01' valve 8 with respect to valve 1 is increased and consequently the valve 8 supplies more charging current to the capacitor 8 than does the valve 1. This produces a reversal of the polarity of the component direct voltage across the capacitor 8, i. e. the polarity is such that the voltage of the terminal 6a becomes negative thereby retarding the firing point of the valve 2 to cut-off or below.

In addition, the increased conductivity of the valve 8 produces an increased voltage drop across the common cathode resistor I 8 thereby making the voltage of the cathode 8b more positive with respect to the voltage of the grid 8c. ously, the increased voltage drop across the This results in retarding.

Further decreases in the amount of light talling upon the cathode in the photo-electric cell. 28 efiects corresponding advances in thefiring point of valve 3 and corresponding increases. in the speed of the motor in that direction.

From the foregoing it is seen that the valve 8 cooperates with the valve 1 to vary the firing point of valve 2 and, similarly, that the valve l4 cooperates with the valve l3 to vary the firing point of the valve 3. In addition, the valves 8 and I4 serve as switching valves to switch the control between the valves 2 and 3 and thereby determine the direction of rotation of the motor in accordance with the magnitude or the signa voltage across the resistors 18 and I9.

It is not essential that a photo-electric cell be utilized to produce a signal voltage for operation of the system. As shown in Fig. 2, any voltage corresponding to a predetermined quantit may be utilized asa signal voltage and impressed between the cathode and grid of the valve 28 which corresponds to the first stage amplifier valve 28 of Fig. 1.

Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the elements shown and described are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A control system for a dynamoelectric machine comprising a; pair of alternating voltage supply conductors, means for controlling the magnitude and polarity of the excitation of said machine comprislng a first pair of electric valves each provided, with an anode; a cathode and a control grid, means for supplying a voltage having a periodically varying component and a'direct component to the grids of said valves comprising a first capacitor connected between the grid and Simultanecathode of one of said valves and a pair of reversely connected electric valves connected in circuit with said capacitor across said supply conductors a second capacitor connected between the grid and cathode of the other or said first pair of valves and a pair of reversely connected electric valves connected in circuit with said second capacitor across said supply conductors, one of each of said pairs of reversely connepted valves being a triode valve having an anode, a cathode and control grid, means for supplying a bias voltage between the grid and cathode of one of said 7 triode valves, means for supplying a signal voltage between the grid and cathode of the other or said triode valves, and a resistor common to both said triode valves and connected between the triodes thereof and one of said supply conductors for efiecting operation of said triode valves as reversing switching valves to advance the firing point of one of said first pair of valves and to retard the firing point of the other of said first pair oi valves.

2. A control system for a dynamoelectric machine provided with a pair of opposed field windings comprising a pair of alternating voltage supply conductors, means for controlling the magnitude and polarity of the excitation of said machine comprising a first pair of electric valves each connected in circuit with a corresponding one of said windings and each provided with an anode, a cathode and a control grid, means for supplying a voltage having'a direct component and a periodically varying component to the grids of said valves comprising, a first capacitor connected between the grid and cathode of one of means 8 tric valves connected in circuit with said capacitor across said supply conductors, a second capacitor connected between the arid and cathode o! the said valves and a pair of reversely connected elecother or said first pair oi valves and a pair of reversely connected electric valves connected in circuit with said second capacitor across said suppl conductors, one or each or said reversely connected pairs of valves being a triode valve provided with an anode, a cathode and a control grid, means for supplying a bias voltage to the grid of one of said triode valves, means for supplying to the grid of the other of said triode valves a variable signal voltage having valves greater and less than a predetermined value and a resistor common to both said triode valves and connected between the cathode thereof and we of said supply conductors for eflecting operation or said triode valves as reversing switching valve for selectively controlling the firing points 01' said first pair of valves to effect selective energlzation of said field windings in response to the magnitude of said signal voltage.

ELMO E. MOYER. DONALD ELDRED. 

